This invention relates to a four-cycle engine and more particularly to an induction system for such an engine that is particularly adapted at achieving open chamber stratification.
It has been proposed to improve the fuel efficiency and exhaust gas emission control of an internal combustion engine by providing a stratified charge combustion process. With a stratified charge combustion process, a stoichiometric fuel/air mixture surrounds the spark plug at the time of ignition. The remainder of the chamber is, however, charged with air and/or fuel at a less than stoichiometric mixture. When the rich mixture in the vicinity of the spark plug is ignited, the remaining weak mixture will also burn due to the rapid transfer of the flame front and the increased pressure in the chamber. Thus, it is possible to operate an engine in this manner at less than full speed and load when the total chamber is charged with a less than stoichiometric mixture.
One method of achieving stratification as heretofore proposed embodies a generally open single combustion chamber in which stratification is achieved. The various methods for employing stratification with open chambers, such as the Texaco Combustion Process and other processes of this general type have required direct cylinder fuel injection. Direct fuel injection is done in such a manner and with such a timing as to achieve stratification and a rich fuel/air mixture in the vicinity of the spark plug at the time of ignition. Such devices, however, have not met any large degree of commercial success due to the high cost of the injection equipment required. Furthermore, it is very difficult with this type of arrangement to insure that the stoichiometric fuel/air patch will be in proximity to the spark gap at the time of injection.
Another method for achieving stratification employs the use of an auxiliary combustion chamber in which the spark plug is position or to which the spark plug is proximate which is charged with a richer fuel/air mixture than the remaining larger portion of the combustion chamber. With this type of engine, the rich fuel/air mixture may be delivered to the auxiliary chamber either by means of a carburetor or by means of a fuel injection system. This type of stratification, however, has several disadvantages. First, because of the use of the auxiliary combustion chamber, the total surface to volume ratio of the combustion chamber (S/V ratio) is increased and heat loss results. Furthermore, there are significant pumping losses in achieving the flow between the auxiliary and main combustion chambers. Furthermore, if a carbureted arrangement is employed, the scavenging of the auxiliary combustion chamber during the exhaust stroke may cause significant loss of fuel and air during the next intake cycle with conditions of valve overlap.
It is, therefore, a principal object of this invention to provide an improved induction system for achieving stratification in an internal combustion engine.
It is another object of this invention to provide an improved open chamber stratified internal combustion engine.
It is a further object of this invention to provide an induction system for an internal combustion engine which permits the use of a carburetor and which will still achieve stratification.
It is yet a further object of this invention to provide an improved, carbureted, stratified charge internal combustion engine wherein no fuel charge is lost due to the scavenging of the chamber.
It has been found that stratification may be achieved in an open chamber engine by providing two separate induction passages, one of which provides the chamber with a richer fuel/air mixture than the other. If the intake passages are made to communicate with the chamber at different times during the intake stroke, it is possible to achieve stratification and yet permit the use of carburetion. That is, it has been found that by providing communication of the leaner fuel/air mixture with the combustion chamber during the initial intake stroke and communication of the richer fuel/air mixture at the end of the intake stroke, it is possible to insure a rich fuel/air mixture in the vicinity of the spark plug at the time of ignition and still permit the use of carburetion and minimize the loss of fuel during scavenging.
It is another object of this invention to provide a simplified induction system which will achieve stratification of the type described.